FIG. 1 illustrates a cable tester 20 that applies a test signal in the form of a frequency sweep test signal VTSWEEP to a cable 10 to thereby measure the length of cable 10. Specifically, frequency sweep test signal VTSWEEP is applied to a transmission end 11 of cable 10 as a series of stepped-up frequency sine waves that travel to a reflection end 12 of cable 10 and are reflected back to the transmission end 11 of cable 10 as a frequency sweep reflected signal VRSWEEP. A frequency-domain reflectometry (“FAR”) system can be used by cable tester 20 to measure the length of cable 10 based on the frequency response of the frequency sweep reflected signal VRSWEEP. Examples of a FAR system include a frequency-modulated continuous wave system (“FMCW”), a standing-wave reflectometry (“SWR”) system and a phase-detection reflectometry (“PDFDR”) system.
A drawback to FAR systems is the time consumption required to execute the sweep frequency points (e.g., 400 frequency points) of the frequency sweep test signal VTSWEEP from its lowest frequency (e.g., 1 MHz) to its highest frequency (e.g., 256 MHz). Thus, a need exists to provide a technique for measuring the length of a cable with minimal frequency points over a reliable frequency range.